Magnetic disk apparatuses as information recording/reproducing apparatuses have been used as chief external memory devices for computers because of their large capacity, high transfer rates, and high-speed random access capabilities. In particular, there is a marked recent trend toward larger capacity magnetic disk apparatuses, the density being increased at an annual rate of 60%. Correspondingly, the size of bit cells recorded in a disk is decreased, leading to a need for even narrower tracks. For example, in order to achieve an areal recording density of 20 to 40 Gbits/in2, a sub-micron track pitch of 0.35 μm or less is expected to be required. Precise and high-speed tracking control is being pursued for the stabilization of signals in recording and reproducing information on such narrow tracks.
A conventional magnetic disk apparatus typically has a head for recording and reproducing information on a disk medium, a slider carrying the head, a head support mechanism for supporting the head via the slider, and a driving means for causing the head to track to a predetermined position on the disk medium via the head support mechanism. In conventional disk apparatuses, the driving means is generally implemented as a single stage of a rotary VCM (voice coil motor).
Such a single-stage driving means imposes some limits to the realization of high-precision tracking for the above-described narrow track pitch on the order of sub-microns. Various techniques have been devised in which a second stage of a micro-movement driving means is used in addition to the first stage or the main driving means. As such a two-stage controlled actuator, a mode in which a head support mechanism (i.e., suspension) is driven, a mode in which a slider is driven, a mode in which a head element is mounted on a slider, and the like, have been devised.
The functions of a head support mechanism of a magnetic disk apparatus include pressuring a slider toward a disk against a force acting on the slider due to the proximity flying, or contact with, a rotating disk, causing the slider to track a waving disk surface, and the like. Accordingly, the head support mechanism is composed of a plurality of members so that these functions are assigned to the individual members. The member for serving the former function is referred to as a load beam. The member for serving the latter function is referred to as a flexure or gimbal (hereinafter referred to as a “flexure”).
Japanese Laid-open Publication No. 9-73746 discloses a head support mechanism including micro-movement driving means such that first and second piezoelectric thin films are provided in parallel on one surface of a load beam in a longitudinal direction thereof, and third and fourth piezoelectric thin films are provided facing the opposite surface. However, in order to obtain a large displacement for enabling tracking in this structure, it is necessary to expand or contract (deform) the piezoelectric thin films against a substantial inplane rigidity, which requires a high driving voltage (e.g., 50 V) because the expansion and contraction directions (displacement direction) of the piezoelectric thin film are within the plane of the piezoelectric thin film.
Japan Society of Mechanical Engineers, the 75th Ordinary General Meeting Conventional Speech Papers (IV) (1998, March 31 to April 3, Tokyo), pp. 208-209 discloses a two-stage controlled actuated mounted on a back face of a slider. This amounts to a driving mode in which piezoelectric ceramics are employed as micro-movement driving means, and in which a multi-layer structure is adopted in order to reduce a driving voltage. A multi-layer structure including a multitude of layers is designed so as to reduce a driving voltage. In this case, too, the expansion and contraction directions (displacement direction) of the piezoelectric ceramics are within the plane of the piezoelectric ceramics multi-layer structure. Therefore, the piezoelectric ceramics need to be expanded or contracted (deformed) against a substantial inplane rigidity, which disadvantageously requires a considerably high applied driving voltage (e.g., 20 V), similar to the above-described conventional example disclosed in Japanese Laid-open Publication No. 9-73746. Since this two-stage controlled actuator is of a type which is mounted on the back face of a slider, a thickness of the magnetic disk apparatus in a height direction thereof is increased, which hinders the reduction in size and thickness of the magnetic disk apparatus.
An applied driving voltage of several tens of volts is required for the above-described conventional micro-movement driving means. Whereas a typical reproduction signal in a magnetic disk apparatus is generally on the order of millivolts, the driving voltage for the above-described conventional micro-movement driving means is on the order of several tens of volts. Therefore, some influence is expected on the reproduction signal due to the driving of the micro-movement driving means.
With the above-described conventional example, it may be difficult to obtain a large displacement for tracking along a tracking direction, or a high driving voltage may be required to obtain a large displacement, indicative of problems associated with a poor driving efficiency.
Furthermore, there are structural disadvantages in view of reduction in size and mass of the magnetic disk apparatus. The present invention was made in order to solve these conventional problems.
An objective of the present invention is to provide: a head support mechanism including micro-movement driving means which realizes high-speed and high-precision tracking so as to be compatible with narrow track pitches required due to an increasing areal recording density while the micro-movement driving means is easy to produce and is driven with a low driving voltage at a practical level; an information recording/reproducing apparatus incorporating the same; and a method of manufacturing the head support mechanism.